The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Can You Start Mounjaro At 5 Mg?
No, you cannot start Mounjaro at 5 mg in the UK. All adults beginning this tirzepatide injection must start at the 2.5 mg starter dose, administered once weekly for the first four weeks. This gradual dose escalation is essential for safety and tolerability. Your prescriber will increase your dose only after you've been on each level for a minimum of four weeks, assuming you're tolerating it well. Understanding the standard Mounjaro dosing schedule helps set realistic expectations and explains why patience is important during the initial treatment phase.
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Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro Dose Titration Works
Mounjaro must be started at 2.5 mg once weekly, regardless of your weight, BMI, or severity of excess weight. This is the standardised starter dose in the UK. After four weeks, if you're tolerating the injection well, your prescriber will increase you to 5 mg. Subsequent escalations follow a similar pattern: 7.5 mg (weeks 9–12), 10 mg (weeks 13–16), 12.5 mg (weeks 17–20), and finally 15 mg (the maximum dose) from week 21 onwards.
Each KwikPen contains four weekly doses of the same strength, so you'll complete one pen before moving to the next dose level. This structured approach allows your body to adapt to the medication and gives you and your prescriber time to monitor side effects and efficacy at each stage.
- Week 1–4: 2.5 mg (starter dose)
- Week 5–8: 5 mg (first escalation)
- Week 9+: Further increases based on tolerance and response
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How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Why Start Low and Escalate Gradually?
Starting at a lower dose and titrating upwards reduces the risk of unwanted side effects and allows your prescriber to find the minimum effective dose for you. Early Mounjaro side effects—such as nausea, vomiting, or diarrhoea—are often mild and tend to improve as your body adjusts. A gradual escalation schedule gives your digestive system time to adapt.
Clinical trials and real-world experience show that this tiered approach improves treatment adherence and tolerability. Some people achieve their weight loss goals at 5 mg or 7.5 mg and don't need the maximum 15 mg dose. By escalating gradually, you avoid unnecessary side effects and find your optimal dose more efficiently. Your GP or prescriber will guide you through each stage based on your individual response.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
What happens if I can't tolerate 2.5 mg Mounjaro?
If you experience severe side effects at 2.5 mg, contact your prescriber immediately. Dose reduction is sometimes possible, though it's unusual. Your prescriber may pause escalation or adjust timing. Never stop or reduce Mounjaro without medical guidance. Side effects often improve with time, but your individual health matters most.
Can I skip ahead to 5 mg if I'm not seeing results on 2.5 mg?
No. You must wait a minimum of four weeks on each dose before escalation, even if you haven't seen weight loss yet. Weight loss results take time—clinical trials measured results over 68+ weeks. Escalating too quickly increases side effect risk without additional benefit. Your prescriber will escalate you on schedule if you're tolerating the dose well.
Is Mounjaro different from Wegovy in terms of starting dose?
Yes. Mounjaro (tirzepatide) starts at 2.5 mg, whereas Wegovy (semaglutide) starts at 0.25 mg. Wegovy requires a longer titration schedule with smaller increments. Mounjaro is a dual GIP and GLP-1 agonist, making it more potent than Wegovy's single GLP-1 mechanism, which is why the starting doses differ.
How long will it take to reach the maximum 15 mg Mounjaro dose?
If you escalate at each four-week interval without pausing, you'll reach 15 mg around week 21. However, many people don't need the maximum dose—your prescriber will assess whether further escalation is necessary based on your weight loss progress and side effect tolerance. Reaching the top dose isn't the goal; finding your effective dose is.
Can my prescriber start me at 5 mg off-label?
Officially, no. UK prescribers follow the licensed dosing schedule starting at 2.5 mg. Off-label prescribing is legal but requires clear clinical justification and is rarely appropriate for weight management. Always discuss your treatment plan with your prescriber. Use our free GLP-1 weight loss calculator to explore projected outcomes at different standard doses.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.